In one example conventional process a photoresist is applied on a substrate and patterned so that some areas of the substrate are exposed. The exposed areas are then implanted with dopants. However, the implantation process may chemically change an outer portion of the photoresist layer so that the outer portion includes tough polymers with single carbon bonds. The chemically changed outer portion of the photoresist layer may make the photoresist layer more difficult to remove using conventional techniques.
One conventional technique includes the use of a plasma ashing process and a wet clean to remove the photoresist. The plasma ashing process creates an ash residue from the photoresist, and the wet clean process removes the residue and any remaining photoresist material. However, the ash residue can be difficult to remove completely with the wet clean, especially in scenarios when the photoresist has been subjected to an implantation process. In some cases, the residue may remain on the substrate after the stripping process is completed, which interferes with formation of subsequent layers and lowers yield. On the other hand, the times/concentrations for the plasma ashing and wet clean can be increased to ensure that more photoresist residue is removed, but such an approach may lead to broken lines on the semiconductor devices. Thus, residue removal and broken lines can sometimes be a trade-off in conventional processes. What is needed is an improved technique to remove photoresist material.